The invention relates generally to dielectric materials and, more particularly, to barium titanate-based compositions that may be used to form dielectric layers in an electronic device such as a multilayer ceramic capacitor.
Barium titanate-based compositions, which include barium titanate (BaTiO3) and its solid solutions, may be used to form dielectric layers in electronic devices such as multilayer ceramic capacitors (MLCCs). The barium titanate-based compositions are typically produced as small particles (e.g., about 1 micron or less) which may be further processed to form a dielectric layer. MLCCs include a series of alternating dielectric and electrode layers which are stacked to form a laminate structure. Certain types of MLCCs utilize nickel-based electrodes. Nickel-based electrodes may provide cost savings over precious metal-based electrodes (e.g., Pd, Agxe2x80x94Pd).
Industry standards exist to qualify the performance of MLCC devices. For example, an MLCC is required to have certain electrical and mechanical properties to achieve X7R specifications or X5R specifications. The X7R specification has a temperature stability requirement (a capacitance at xe2x88x9255xc2x0 C. and at 125xc2x0 C. that varies less than +/xe2x88x9215% from the capacitance at 25xc2x0 C.) and a dissipation factor requirement (less than 3.5% at 1.0 Vrms). The X5R specification has a temperature stability requirement (a capacitance at xe2x88x9255xc2x0 C. and at 85xc2x0 C. that varies less than +/xe2x88x9215% from the capacitance at 25xc2x0 C.) and a dissipation factor requirement (less than 5.0% at 1.0 Vrms).
Pure barium titanate (BaTiO3) undergoes several phase transformations over the temperature range of xe2x88x9255xc2x0 C. and 125xc2x0 C. which can cause a change in capacitance. For example, the tetragonal-cubic transformation that occurs near 125xc2x0 C. typically causes an anomalous increase in capacitance on the order of 300-500% the value of the dielectric constant at 25xc2x0 C. Thus, pure barium titanate generally cannot be used to form dielectric layers in MLCCs that satisfy the X7R or X5R specifications.
Dopants may be added to pure barium titanate in order to improve certain electrical properties of MLCCs including increasing temperature stability and decreasing dielectric loss. Typically, the dopants are metallic compounds, often in the form of oxides or hydroxides. With the addition of dopants, it is possible to form compositions which can form dielectric layers of MLCCs that satisfy the X7R or X5R requirements. However, sometimes, such compositions can have other disadvantages such as a relatively low capacitance and/or high dielectric loss which can sacrifice the performance of MLCCs which include dielectric layers formed from the compositions.
The invention provides dielectric compositions, methods of forming the same, and capacitors that include dielectric layers formed from the dielectric compositions.
In one aspect the invention provides a dielectric composition. The dielectric composition comprises a barium titanate-based material, a rare earth metal compound, a manganese compound, an alkaline earth metal compound, a hexavalent metal compound, and a silicate-based compound.
In another aspect, the invention provides a dielectric composition. The dielectric composition comprises barium titanate, yttrium which comprises between about 0.10% and about 2.5% of the total weight of the dielectric composition, manganese which comprises between about 0.01% and about 0.20% of the total weight of the dielectric composition, magnesium which comprises between about 0.01% and about 0.50% of the total weight of the dielectric composition, molybdenum which comprises between about 0.01% and about 0.20% of the total weight of the dielectric composition, and barium silicate which comprises between about 0.50% and about 5.0% of the total weight of the dielectric composition.
In another aspect, the invention provides a dielectric composition. The dielectric composition comprises barium titanate-based particles. The barium titanate-based particles have a coating comprising a rare earth metal compound, a manganese compound, an alkaline earth metal compound, a hexavalent metal compound, and a silicate-based compound.
In another aspect, the invention provides a capacitor. The capacitor includes at least one electrode layer and at least one dielectric layer. The dielectric layer comprises a barium titanate-based material, a rare earth metal compound, a manganese compound, an alkaline earth metal compound, a hexavalent metal compound, and a silicate-based compound.
In another aspect, the invention provides at least one electrode layer and at least one dielectric layer. The dielectric layer comprises a dielectric composition. The dielectric composition comprises the dielectric composition comprises barium titanate, ytrium, manganese, magnesium, molybdenum, and barium silicate. Yttrium comprises between about 0.10% and about 2.5% of the total weight of the dielectric composition. Manganese comprises between about 0.01% and about 0.20% of the total weight of the dielectric composition. Magnesium comprises between about 0.01% and about 0.50% of the total weight of the dielectric composition. Molybdenum comprises between about 0.01% and about 0.20% of the total weight of the dielectric composition. Barium silicate comprises between about 0.50% and about 5.0% of the total weight of the dielectric composition.
In another aspect, the invention provides a method of forming a dielectric composition. The method includes forming a coating on barium titanate-based particles. The coating comprises a rare earth metal compound, a manganese compound, an alkaline earth metal compound, a hexavalent metal compound, and a silicate-based compound.
Other advantages, novel features, and aspects of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying figures, and from the claims.